Quantitative studies of normal and abnormal human postural control mechanisms will continue using simultaneous center-of-force recordings with controlled visual and proprioceptive inputs. Visual-vestibular and proprioceptive-vestibular interactions will be studied in normal and abnormal subjects. Gastrocnemius-tibialis anterior EMG recordings will be used with galvanic vestibular stimuli to study vestibulo-spinal control in subjects with unilateral vestibular system deficits. Results will be used to further refine posturographic techniques for clinical diagnostic evaluation of patients complaining of spatial disorientation.